1. Technical Field
This invention relates generally to toner concentration control systems used in electrostatographic marking engines.
2. Background Art
With the development of electrostatographic marking engines using more than one color, the need arises to monitor and control the toner concentration in more than one development mixture. Since manufacturing costs have to be minimized, much engineering effort focuses on developing cost effective solutions at uncompromised performance. To this end, it has been proposed that cost effective control of toner concentrations in more than one developmemt mixture can be accomplished by using only one toner monitor. See for example commonly assigned U.S. patent application Ser. No. 07/632,677, filed in the names of A. S. Kroll and W. Chang on Dec. 24, 1990.
In order to obtain a statistically significant toner monitor reading, particularly in conjunction with the hard magnetic materials used in some development mixtures, one must tightly control environmental effects, the mechanical interface between the development mixture and the toner monitor, and/or the variation in electrical performance of the toner monitor. Since environmental conditions are largely unpredictable, a rather large range in operating temperature (i.e., 10.degree. C. to 35.degree. C.) has to be considered in the design to make the product attractive for general consumer application. Even such a limited operating temperature range may often cause a shift in toner monitor readings V.sub.M equal to a change of several percent toner concentration in the development mixture. Therefore, the statistical significance of the monitor reading V.sub.M over the full range of operating temperature, is questionable.
Kroll and Chang proposed the use of an environmentally stable reference member which, when presented to the toner monitor, simulates the magnetic permeability of the actual development mixture. The resultant temperature stable reference reading is used to correct the toner concentration readings obtained from the development mixture under any operating environment.
Since many different toner monitors will be used, variations between toner monitors will make the development of one algorithm suited to correct the temperature effects of all toner monitors over the lifetime of the program very difficult, if not impossible. Because it is not economical to characterize every single toner monitor in a manufacturing environment in order to match the algorithm applying the temperature correction, assumptions regarding the monitor's performance and performance compromises will have to be made; making the statistical significance of the toner monitor reading again questionable.